1. Statement of Related Cases
The present application is related to the companion applications filed on the same date herewith and commonly assigned U.S. patent application Ser. No. 815,092 now U.S. Pat. No. 5,273,799 entitled "A Shaped-Altered Seamed Imaging Flexible Member and Method of Constructing a Flexible Imaging Sheet"; and U.S. patent application Ser. No. 815,086 entitled "A Seamed Imaging Flexible Member Having Generally Undetectable Seam Defects and Method of Constructing a Flexible Imaging Sheet".
2. Field of the Invention
This invention relates generally to a flexible member for use within an electrophotographic printing system, and more specifically, the present invention is directed to an improved scribed seamed imaging flexible member and a method for constructing a flexible imaging sheet.
3. Description of the Prior Art
The basic xerographic process comprises exposing a charged imaging photoconductive member, typically a flexible member or a non-flexible drum, to a light image of an original document. The irradiated areas of the photoconductive surface are discharged to record thereon an electrostatic latent image corresponding to the original document. A development system, thereupon, moves a developer mix of carrier granules and toner particles into contact with the photoconductive surface. The toner particles are attracted electrostatically from the carrier granules to the latent image forming a toner powder image thereon. Thereafter, the toner powder image is transferred to a sheet of support material. The sheet of support material then advances to a fuser which permanently affixes the toner powder image thereto.
There exists a wide variety of flexible members which can be utilized within an electrophotographic machine that utilizes the basic xerographic process. Of these, the most prominent in importance is the electrophotographic imaging member. The methods for constructing a flexible sheet and problems encountered therewith that are described hereinafter pertain in particular to an imaging member, and more specifically, a photoconductive member. However, a wide variety of flexible members exist, for example, transfer members, ionographic members, dielectric members, and other members which include a wide variety of coating or special application layers. The following discussion pertaining to an imagining member applies equally to the above-mentioned members as with respect to the problems encountered with the construction and utilization thereof.
An electrophotographic imaging flexible member may be provided in a number of forms. For example, the imaging member may be a homogeneous layer of a single material, such as vitreous selenium, or it may be a composite layer containing a photoconductor and another material. One type of composite imaging member comprises a layer of finely divided particles of a photoconductive inorganic resin binder. The photogenerating layer is capable of photogenerating holes and injecting the photogenerated holes into the charge transport layer.
As more advanced, higher speed electrophotographic copiers, duplicators and printers were developed, degradation of image quality was encountered during extended cycling. Moreover, complex, highly sophisticated duplicating and printing systems operating at very high speeds have placed stringent requirements including narrow operating limits on photoreceptors. For example, the numerous layers found in many modern photoconductive imaging members must be highly flexible, adhere well to adjacent layers, and exhibit predictable electrical characteristics within narrow operating limits to provide excellent toner images over many thousands of cycles. One type of multilayered photoreceptor that has been employed as a belt in electrophotographic imaging systems comprises a substrate, a conductive layer, a blocking layer, an adhesive layer, a charge generating layer, a charge transport layer, and a conductive ground strip layer adjacent to one edge of the imaging layers. This photoreceptor may also comprise additional layers, such as an anti-curl back coating layer and an optional over-coating layer.
The electrophotographic imaging flexible member may be fabricated from a sheet cut from a web. The sheets are generally rectangular in shape. All sides may be of the same length, or one pair of parallel sides may be longer than the other pair of parallel sides. The sheets are formed into a belt by joining overlapping opposite marginal end regions of the sheet. A seam is typically produced in the overlapping marginal end regions at the point of joining. Joining may be effected by any suitable means. Typical joining techniques include welding (including ultrasonic), gluing, taping, pressure heat fusing, and the like. Ultrasonic welding is generally the preferred method of joining because of its speed, cleanliness (no solvents) and production of a thin and narrow seam. In addition, ultrasonic welding is preferred because it causes the generation of heat at the contiguous overlapping marginal end regions of the sheet to maximize melting of one or more layers therein.
When ultrasonically welded into a belt, seams in some multilayered imaging flexible members can delaminate during fabrication when larger webs are slit into smaller belt size sheets. Further, after the sheets are welded into belts, the belts tend to delaminate during extended cycling over small diameter support rollers or when subjected to lateral forces caused by rubbing contact with stationary web edge guides of a belt module during cycling. Seam delamination is further aggravated when the belt is employed in electrophotographic imaging systems utilizing blade cleaning devices. In addition, belt delamination is encountered during the web slitting operations fabricating belt photoreceptors from wide webs. Alteration of the materials in the various belt layers, such as the conductive layer, hole blocking layer, adhesive layer, charge generating layer, and/or charge transport layer to reduce delamination is not easily accomplished The alteration of the materials may adversely affect the overall electrical, mechanical and other properties of the belt, such as residual voltage, background, dark decay, flexibility and the like.
For instance, the imaging flexible member in an electrophotographic machine can be a photoreceptor belt fabricated by the lap-joined ultrasonic welding of the opposite ends thereof. In the ultrasonic seam welding process, ultrasonic energy transmitted to the overlap region is used to melt the sheets of photoconductive, substrate and/or coating materials into a seam. The ultrasonic welded seams of multilayered photoreceptor belts are relatively brittle and low in strength and toughness. The joining techniques, particularly the welding process, can result in the formation of a flashing or splashing that projects beyond the sides and the edges of the seam in the overlap region of the photoreceptor belt. As a result of the splashing, the imaging flexible member is about 1.6 times thicker in the seam region than that of the remainder thereof (in atypical example, 188 microns vs. 116 microns).
The photoreceptor belt in an electrophotographic imaging apparatus undergoes strain as the belt is cycled therethrough over a plurality of rollers therein. The excessive thickness of the photoreceptor belt in the seam region due to the presence of the splashing results in a large induced bending strain as the seam goes over each roller. Generally, small diameter support rollers, highly desirable for simple, reliable copy paper stripping systems, are used in the electrophotographic imaging apparatuses having a photoreceptor belt system operating in a very confined space. Unfortunately, the small diameter rollers, e.g., less than about 0.75 inches (19 millimeters) in diameter, raise the threshold of the mechanical performance criteria to such a high level that the photoreceptor belt seam failure can become unacceptable for the multilayered belt photoreceptors. For example, when bending over a 19 millimeter roller, a XEROX.RTM. standard Active Matrix Material belt seam splashing may develop a 0.96% tensile strain due to bending. This compares with a 0.59% induced bending strain which may develop within the rest of the photoreceptor belt. The 0.96% tensile strain in the seam splashing region of the belt, thus represents a 63% increase in stress placed upon the seam splashing region of the belt.
Under dynamic fatiguing conditions, the seam provides a focal point for stress concentration and becomes the initial point of failure in the mechanical integrity of the belt. The splashing, thus, tends to shorten the life of the seam and, thereby, the life of the flexible member in copiers, duplicators, and printers. There is a need for improving the flexible members to have a seam which can withstand greater fatiguing conditions.
The following disclosures may be relevant to various aspects of the present invention:
U.S. Pat. No. 2,679,305; Patentee: S. Gunthorp; Issued: May 24, 1954.
U.S. Pat. No. 3,493,448 Patentee: Powell et al.; Issued: Feb. 3, 1970.
U.S. Pat. No. 4,410,575; Patentee: Obayashi et al.; Issued: Oct. 18, 1983.
U.S. Pat. No. 4,430,146; Patentee: E. Johnson; Issued Feb. 7, 1984.
U.S. Pat. No. 4,532,166; Patentee Thomsen et al.; issued: Jul. 30, 1985.
U.S. Pat. No. 4,648,931; Patentee: O. Johnston; Issued: Mar. 10, 1987.
U.S. Pat. No. 4,838,964 Patentee: Thomsen et al.; Issued: Jun. 13, 1989.
U.S. Pat. No. 4,878,985 Patentee: Thomsen et al.; Issued: Nov. 7, 1989.
U.S. Pat. No. 4,883,742 Patentee: Wallbillich et al.; Issued: Nov. 28, 1989.
U.S. Pat. No. 4,937,117; Patentee: Yu; Issued: Jun. 26, 1990.
U.S. Pat. No. 4,959,109; Patentee: Swain et al.; Issued: Sep. 25, 1990.
U.S. Pat. No. 4,968,369; Patentee: Darcy et al.; Issued: Nov. 6, 1990.
U.S. Pat. No. 5,021,109; Patentee: Petropoulous et al.; Issued: Jun. 4, 1991,
Co-pending U.S. patent application Ser. No. 07/634,365; Applicant: Swain et al.; Filed: Dec. 27, 1990.
The relevant portions of the foregoing disclosures may be briefly summarized as follows:
U.S. Pat. No. 2,679,305 discloses a method of improving the durability of a structural joint formed by overlapping and bonding two metallic members. In order to more readily permit greater extension or deflection at the joint and, thereby, prevent the formation of high stress concentration at the joint when the structure is loaded, grooves are formed in the surfaces of the joined members parallel and proximate to the edges thereof on both sides of the joint.
U.S. Pat. No. 4,883,742 discloses a joining of an end and/or lateral areas of thermoplastically processed photosensitive layers. The end and/or lateral areas of photosensitive layers are overlapped to avoid bubbles and air cavities between the end and/or lateral areas. The overlapped area is then heated under pressure to firmly join the areas together. The joined photosensitive layer is then treated and smoothed to shape it to size.
U.S. Pat. No. 4,410,575 discloses a method of lap welding fabrics together by superposing two end portions of one or two fabrics on each other with an interposing bonding tape between the superposed two end portions. The method includes applying a high frequency wave treatment and/or heat treatment by pressing at least one of the superposed end portions to melt the interposed portion of the bonding tape in order to lap melt the fabrics to each other. At least one side edge portion of the tape extends outwardly over an edge of the end portion which is deformed from the forces absorbed when the heat treatment and frequency wave treatment are applied. The fabrics may be made of any fibers or natural fibers.
U.S. Pat. No. 3,493,448 discloses a method of splicing photographic film by an ultrasonic welding apparatus which includes steps comprising sandblasting the ends to be welded and chilling the fused ends to be fused together. The ends of the photographic film are overlapped and compressed together. Heat is introduced into the film ends for fusing together.
U.S. Pat. No. 4,968,369 discloses an apparatus and process for fabricating belts wherein the leading edge and the trailing edge are overlapped to form a lap joint. Welding of the belt results in flashings at each end of the welded lap joint. A punch cutter is utilized to remove weld flashings at each end of the welded belt lap joint.
U.S. Pat. No. 4,878,985 and U.S. Pat. No. 4,838,964 each disclose an apparatus and a process for fabricating belts wherein the leading edge and the trailing edge are overlapped to form a loop of a web segment loosely suspended from the joint formed thereby. The web is sheared to form a leading edge free of defects. An ultrasonic belt welding station comprising an ultrasonic horn and transducer assembly is utilized in the fabrication of the belt.
U.S. Pat. No. 4,937,117 discloses a flexible belt fabricated from a substantially rectangular sheet having a first edge joined to a second parallel edge to form a seam. Flashings at the ends of the welded seam of the belt are removed by means of a notching device capable of cutting the desired elongated shape.
U.S. Pat. No. 4,959,109 discloses a process and apparatus for fabricating a unitary belt comprising two rotatable mandrels and a wrapping station. A web is wrapped around each rotatable mandrel whereat the web is severed to form a trailing edge. A wrapping station overlaps a leading edge of the web to form a belt having a seam.
U.S. Pat. No. 4,532,166 discloses a welded web and a process for forming the web. The web may be formed by a process in which a web having a first edge is provided. At least one aperture is formed in at least the first edge. The first edge is then overlapped on an exposed surface of a second edge. Ultrasonic welding may be used to raise the temperature of at least the region of contiguous contact adjacent the aperture. Thermoplastic material from the second edge at least partially fills the aperture, thereby bonding the first edge to the second edge.
U.S. Pat. No. 4,648,931 discloses a method of forming a bead seal in a biaxially oriented polymer film by heat bonding. The method consists of pressing together web layers in a sealing zone, a selected segment of the pressed web being heated above the bonding temperature of the plastic while adjacent web segments are maintained below that temperature. The heated web segment has a relatively lower surface friction than the surfaces pressing the adjacent web segment. The layers of the heated segment of the web are physically unrestrained against shrinking during heating and are allowed to shrink back to their preoriented molecular configuration while the adjacent segment is restrained against movement. A hermetic bead seal is thus formed between the web layers.
U.S. Pat. No. 4,430,146 discloses a belt splicing method and apparatus. The apparatus comprises pairs of longitudinal bars on which are respectively mounted platen heating assemblies. One bar is centrally supported pivotally on a clamping arrangement and the other bar is removably connected with the clamping arrangement in a manner permitting pivotable disposition of the bars with their platens in opposed facing parallel relation at various spacings. The apparatus facilitates a new belt splicing method eliminating the conventional need to use supplementary liquid thermoplastic material to effect bonding of the belt ends. By this process, a new belt splice is provided with the spliced ends being fused together with their respective thermoplastic material.
U.S. Pat. No. 5,021,109 discloses a process for preparing a multilayered sheet to form a flexible belt. A tubular sleeve of polymeric material is heated to at least apparent glass transition temperature. The tubular sleeve is placed about a mandrel and treated with one or more layers. The sleeve is reheated, then removed from the mandrel. A seamless belt, having a predetermined inner circumference, is formed.
Co-pending U.S. patent application Ser. No. 07/634,365 discloses a process for coating belt seams with hardenable coatings containing film forming polymers. A smooth liquid coating comprises a hardenable film forming polymer on the welded seam. The coating, substantially free of fugitive solvent, is hardened to form a smooth solid coating on the seam.